The present application relates in general to the recycling of scrap broad goods and, in particular, to the recycling of scrap broad goods containing thermoplastic stabilizer materials.
Broad goods may include a wide variety of fabrics and other materials having a plurality of individual fibers or filaments bundled together to form a tow, or “flattened” (rather than twisted) yarn. For example, in some cases, a tow may include a bundle of 3,000, 6,000, 12,000 or 24,000 fibers or filaments, depending on the desired application. A plurality of tows, in turn, are frequently woven together to form a sheet of reinforcement fibers.
One example category of broad goods are fiber-reinforced resin matrix composites, such as carbon fiber or fiberglass, which may be used in a variety of applications, including aircraft manufacturing. In some cases, such fiber-reinforced resin matrix composites are formed by arranging and securing dry structural reinforcement fibers (as a fabric or a uni-directional material) in a mold, injecting or infusing resin matrix into the mold, and curing the resin matrix to harden the composite. The dry fibers can be secured in position by stitching, stapling or weaving a thermoplastic into the reinforcement fibers, or interlayering a thermoplastic veil or scrim between layers of fibers. When thermoplastic is added to the fibers (by, for example, electrospinning the veil or scrim to a sheet of fiber), it stabilizes the position of the fibers at the tow level for the resin impregnation and curing process.
During the manufacture of a given composite part, desired pieces, such as ply cutouts, are frequently cut from one or more full sheets of fabric, leaving behind scrap pieces that cannot be used because they may be too small or of the wrong dimensions and fiber orientations for a new ply. Even so, the scrap pieces of composite material often include valuable reinforcement fibers that cannot be used in the finished part. However, the use of thermoplastic veils or scrims increases the difficulty of reclaiming and recycling the reinforcement fibers in the scrap fabric to the point that thermoplastic-containing reinforcement fibers are often discarded rather than being recycled. For example, when the scrap material is cut into pieces, individual fibers frequently tend to pull away from the tows in the fabric. As a result, large scrap fabric pieces tend to fray around the edges, and small scrap fabric pieces tend to fall apart into individual fibers. Attempting to remove the thermoplastic from the fibers is generally not time or cost effective.
Even when thermoplastics are not used, recycled dry reinforcement fibers are often used only in low-value applications because the alignment and structure of the fibers is lost. For example, dry reinforcement fibers may be recycled into random fiber injection molding compounds or milled into very short fiber reinforcements.